1. Field of the Invention
This invention relates to an image sensor package structure and method for making the same, and more particularly to a leadless image sensor package structure and method for making the same.
2. Description of Related Art
As the development of multimedia is flourishing recently, the use of digital image has been more and more frequent, consequently, the corresponding requirements for image process devices are increasing. Many digital image products used nowadays including video camera, PC digital video camera, and even optical scanner and visual telephone etc. acquire images by the use of image sensor. The image sensor including Charge Coupled Device (CCD) and Complementary Metal-Oxide Semiconductor (CMOS) sensor etc. can sensitively receive light beam transmitted by the image and convert into digital signal. Since image sensor needs to receive light source, its package type is quite different from that of any common electronic product.
Conventional image sensor package employs Plastic Quad Flat Package (PQFP) as the package structures disclosed in U.S. Pat. No. 5,523,608 and U.S. Pat. No. 5,529,959. But because of their relatively good size, they are not adequate for the trend of high integration in the near future. Besides, a lot of conventional image sensors employ ceramic carrier such as ceramic Leadless Chip Carrier (LCC) as disclosed in U.S. Pat. No. 5,898,218 and U.S. Pat. No. 5,270,491. Although the ceramic carrier having feature of relatively good in sealing can prolong the service life of the image device, it can""t meet the demand in the market. This is because that ceramic carrier is high in manufacturing cost and is tedious and complicated in manufacturing process. There is another kind of plastic package with its carrier that makes use of laminated substrate to form a type similar to a leadless carrier as disclosed in U.S. Pat. No. 5,811,799. Although this kind of package can reduce its size, the carrier of the package makes of such material as flame-retardant epoxy glass fabric composite resin, e.g. FR-4, FR-5, or Bismaleimide-Triazine (BT). As these kinds of material are relatively high in cost, this kind of package can""t meet the requirements of the market demand either.
The invention is directed to an improved leadless image sensor package that can significantly lower the cost by using lead frame and mold packaging material to form a carrier.
The invention is also directed to an improved leadless package structure that can provide compact package so as to increase package density.
The invention is further directed to an improved method of making a leadless package structure that is simple in manufacturing process so as to increase the production yield and to adapt to mass production.
A leadless image sensor package constructed on a lead frame includes a die pad and a plurality of leads disposed at the periphery of the die pad. A molding compound, disposed on the top surface of the lead frame and being surrounding the die pad on the periphery of the lead frame, fills the clearance between the die pad and the leads and exposes, on the top surface, the die pad and the wire-bonding portion of the leads. Moreover, the lead frame and the molding compound constitute a xe2x80x9cchip containing spacexe2x80x9d with chip set therein. Further, the chip with its back surface attached to the top surface of the die pad makes use of the wires to electrically connect to the bonding pad and the top surface of the wire-bonding portion, thereafter, a transparent lid is used to cap and seal the xe2x80x9cchip containing spacexe2x80x9d.
In the light of the foregoing leadless image sensor package structure, the invention also provides a corresponding method for making the same. The method includes: providing a lead frame, having a plurality of package units, each of the units includes at least a die pad and a plurality of leads disposed at the periphery of the die pad; performing a molding process to form a molding compound on the first surface of the lead frame and being surrounding the outer edge of the lead frame, filling the clearance between the die pad and the wire-bonding portion of the leads, as well as exposing, on the first surface, the die pad and the wire-bonding portion of the leads, thus, to make the lead frame and the molding compound form a xe2x80x9cchip containing spacexe2x80x9d in each of the package unit; performing a chip attaching process to set the chips in the xe2x80x9cchip containing spacexe2x80x9d to attach, with the back surface of the chip, to the first surface of the corresponding die pad ; performing a wire-bonding process by the use of a plurality of wires, to electrically connect respectively to the bonding pads and the top surface of the wire-bonding portion; performing a sealing process to seal respectively the xe2x80x9cchip containing spacesxe2x80x9d by a transparent material; and performing a singulating process to separate the package units.
In accordance with an embodiment of the invention, on the bottom surface, a stepped structure is built at the wire-bonding portion of the leads and at the periphery of the die pad such that the molding compound covers a relatively thinner portion on the bottom surface, or the die pad can be designed in such a way that its thickness is thinner that of the leads to make the molding compound cover the bottom surface of the die pad so as to enhance the bondability between the lead frame and the molding compound. In the molding process, the top mold clamps the top surface of the die pad and the wire-bonding portion while the bottom surface clamps the whole bottom surface to prevent the residual xe2x80x9cflashxe2x80x9d in order to increase the product""s reliability and simplify the fabrication process.
Moreover, the transparent lid disposed at the top end of the xe2x80x9cchip containing spacexe2x80x9d and fixed to the molding compound, can be a transparent glass plate or a transparent plastic plate. The transparent lid can also be a transparent liquid material to be filled in the xe2x80x9cchip containing spacexe2x80x9d and gone through a curing process to complete the package molding process. An array type is used for the package units to tightly dispose them together and to make them adjacent one another, and a punching method is employed to separate the package units. Besides, a strip type of disposition can also be employed and a constant space is kept. And for singulating process, a punching method is also employed to separate the package units.
Since the package structure of the invention directly uses the bottom surface of the lead to be the external electrical connection to form a leadless structure, the package structure can increase the package density. Besides, since the package structure of the invention uses lead frame and molding compound to form a carrier, thereby, the package structure of the invention can significantly lower the product""s cost and facilitate a mass production.